Defect inspection method and device using same

ABSTRACT

A defect inspection device inspecting a sample includes a movable table on which the sample as an inspection object and a pattern chip are mounted, an illumination light irradiation unit which irradiates a surface of the sample or a surface of the pattern chip with linearly-formed illumination light, a detection optical system section where a plurality of detection optical systems are disposed at a plurality of positions above the table and which detect images of scattered light generated from the sample, and a signal processing unit which processes detected signals to detect a defect of the sample surface, and a plurality of repeating patterns for generating the scattered light according to positions of the objective lenses of the plurality of detection optical systems of the detection optical system section when the linearly-formed illumination light is irradiated by the illumination light irradiation unit are periodically formed in the pattern chip.

BACKGROUND

The present invention relates to a defect inspection method applied to adevice or the like which optically inspects defects, extraneousmaterials, or the like of a fine pattern formed on a sample through athin film process typified by a semiconductor manufacturing process or aflat panel display manufacturing process and a device using the defectinspection method.

As a related art in the field of the invention, JP 2012-21994 A (PatentDocument 1) discloses a technique of irradiating a sample withlinearly-formed illumination light and simultaneously detectingscattered light generated from the sample withthree-directionally-arranged detectors, and processing signals outputfrom the detectors to detect the defects on the sample. In addition, JP5-137047 A (Patent Document 2) discloses a focus detection method and afocus detection device using a specific pattern or a specific objectimage for the purpose of easily sensing a focus position of an opticalsystem. In addition, JP 2006-47308 A (Patent Document 3) discloses anoptical system including a plurality of detection systems simultaneouslydetecting reflected light or scattered light from an illuminatedposition.

CITATION LIST Patent Document

Patent Document 1: JP 2012-21994 A

Patent Document 2: JP 5-137047 A

Patent Document 3: JP 2006-47308 A

SUMMARY

If a detection optical system detecting reflected light or scatteredlight from defects has a high resolution, defect detection sensitivityis improved. Therefore, optical design is made so that a resolutionclose to a diffraction limit can be obtained by greatly suppressing awavefront aberration of the detection optical system. In this manner, inorder to maintain stable performance for a long time by using an opticalsystem having a highly advanced design, an inspection object needs to bepositioned to a focus position of the detection optical system at a highaccuracy.

With respect to the problem of implementing the above technique, thereflective index of air is influenced to be changed by the ambienttemperature or the atmospheric pressure, and the focus position of thedetection optical system is varied.

Similarly, in the off-axis-type focus detection system, due to theinfluence of the ambient temperature or the atmospheric pressure, anerror occurs in the focus detection value.

A focus error caused by thermal expansion occurs due to a variation ofmembers fixing the detection optical system and the off-axis focusdetection system or a variation of the position.

In a case where there are a plurality of detection optical systems,since the variation of the focus position of the above-describedproblem 1) occurs in each detection system, it is difficult to align theobject point of each detection optical system.

Since the above-described problems are mainly caused by the variation intemperature and atmospheric pressure of the periphery of the opticalsystems, a structure design for greatly suppressing the variation or atemperature control design for stabilizing temperature is made. However,due to influence of heat releasing of motors, electric circuits, and thelike which are present with an optical system in the same chamber and avariation in atmospheric pressure according to weather conditions, theproblems cannot be managed in a negligible level.

In contrast, Patent Document 1 does not disclose consideration of theabove-described problems 1) to 4).

On the other hand, Patent Document 2 discloses a method of searching forand selecting a pattern similar to a template pattern registered forsensing a focus of an object from an image detected in a detectionoptical system and determining a focusing position from a correlationvalue of the selected pattern and the template pattern while performingstepwise movement of a height of the object. However, in the example ofa semiconductor wafer as an inspection object, the patterns aredifferent according to generations of product types (memory products,logic products) or wiring nodes, and the number of layers in amulti-layered structure, wiring materials of the layers, pattern widths,and the like are different. Therefore, there is no pattern similar tothe template pattern, and the focusing position cannot be determined.Otherwise, in order to search for the pattern similar to the templatepattern, a wide range needs to be searched, so that there is a problemin that a long time is needed until the determination of the focusingposition is completed. Namely, Patent Document 2 does not also considerthe performing of the defect inspection by solving the problems such asthe above-described problems 1) to 4).

In addition, Patent Document 3 discloses a configuration of performingspot illumination of a surface of a wafer and detecting reflected lightor scattered light by using plurality of detection systems. In thisconfiguration, in order to stably detect an image with a highresolution, the surface of the wafer is illuminated with focused spotlight, and the reflected light or the scattered light needs to bedetected by the detection optical system which is focused on the spot.However, as described in the above-described problems 1) to 4), due tothe variation in temperature of the periphery of the optical system,shift between the focal plane of the illumination system and the waferor the variation in the focus position of each detection system occurs.The shift between the focal plane of the illumination system and thesurface of the wafer causes the increase in the size of the spotillumination on the surface of the wafer, so that a spatial resolutionis deteriorated. Accordingly, the defect detection sensitivity isdeteriorated. In addition, due to the shift between the spot on theilluminated wafer and the focus of each detection system, the reflectedlight or the scattered light from the illuminated area spreads over theimage plane of each detection system. Therefore, there is a problem inthat the reflected light or the scattered light reaches areas outsidethe light-receiving areas of respective light-receiving elements so asnot to be detected. As measures for this problem, expansion of thelight-receiving areas may be considered. However, since a problem thatdark current of the elements and shot noise are increased occurs, thelight-receiving areas cannot be easily expanded. Namely, Patent Document3 does not also consider the performing of the defect inspection bysolving the problems such as the above-described problems 1) to 4).

The invention is to provide a defect inspection method capable ofsolving the above-described problem of the related art and maintainingstable performance for a long time by using an optical system having ahighly advanced design and a device using the defect inspection method.Namely, the invention is to provide a defect inspection method capableof implementing highly-sensitive, stable inspection by allowinginspection surface and a focus of illumination light and focuses of aplurality of detection optical systems to be stably coincident with eachother with respective depths of focuses and by stably detectinghigh-resolution images by using the plurality of detection opticalsystems and a device using the defect inspection method.

In order to solve the above-described problems, in the invention, adefect inspection device inspecting a sample includes: a movable tableon which the sample as an inspection object and a pattern chip aremounted; an illumination light irradiation unit which irradiates asurface of the sample or a surface of the pattern chip mounted on thetable with linearly-formed illumination light; a detection opticalsystem section where a plurality of detection optical systems includingan objective lens and an image sensor are disposed at a plurality ofpositions above the table and which allows images of scattered lightincident on respective objective lenses of the plurality of detectionoptical systems disposed at the plural sites among the scattered lightgenerated from the sample which is irradiated with the linearly-formedillumination light by the illumination light irradiation unit to befocused on the respective image sensors to be detected;

and a signal processing unit which processes signals detected by theplurality of detection optical systems of the detection optical systemsection to detect a defect of the sample surface, wherein a plurality ofrepeating patterns for generating the scattered light according topositions of the objective lenses of the plurality of detection opticalsystems of the detection optical system section when the linearly-formedillumination light is irradiated by the illumination light irradiationunit are periodically formed in the pattern chip.

In addition, in order to solve the above-described problems, in theinvention, a defect inspection method of inspecting a sample includes:irradiating a pattern chip which is mounted on a table and in which aplurality of repeating patterns are periodically formed withlinearly-formed illumination light; detecting images of scattered lightincident on respective objective lenses of a plurality of detectionoptical systems which include the objective lenses and image sensors andare disposed at a plurality of positions above the table among thescattered light generated from the pattern chip which is irradiated withthe linearly-formed illumination light by using the respective imagesensors of the plurality of detection optical systems; adjustingpositions of the respective image sensors with respect to thelinearly-formed illumination light irradiated on the pattern chip byusing detection signals of the images of the scattered light detected bythe respective image sensors; and irradiating the sample as aninspection object mounted on the table with the linearly-formedillumination light, detecting images of scattered light incident on theobjective lenses of the plurality of detection optical systems among thescattered light generated from the sample by using the respective imagesensors of the plurality of detection optical systems, and processingsignals detected by the respective image sensors, thereby detecting adefect on the sample.

According to the invention, it is possible to allow an inspectionsurface with a focus of illumination light and focuses of a plurality ofdetection optical systems to be stably coincident with each other withinrespective depths of focuses. Accordingly, it is possible to stablydetect high resolution images by using the plurality of detectionoptical systems, and thus, it is possible to implement high-sensitivitystable inspection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram illustrating a whole configuration of aninspection device according to a first embodiment of the invention.

FIG. 1B is a flowchart illustrating an inspection procedure according tothe first embodiment of the invention.

FIG. 1C is a flowchart illustrating a flow of a detailed process of S104in a process flow of FIG. 1B.

FIG. 2 is a front diagram of a detection optical system for explaining afocus variation of the detection optical system of the inspection deviceaccording to the first embodiment of the invention.

(a) of FIG. 3 is a perspective diagram of a hemispherical surfaceillustrating an incidence position of an illumination light on thehemispherical surface of a wafer and an emission position of positivelyreflected light from the wafer, (b) is a plan diagram of a hemisphericalsurface illustrating a line-and-space pattern allowing diffracted lightto be incident on an aperture 204 of an objective lens 60, (c) is a plandiagram of a hemispherical surface illustrating a line-and-space patternallowing diffracted light to be incident on an aperture 210 of anobjective lens 40, (d) is a plan diagram of a hemispherical surfaceillustrating a line-and-space pattern allowing diffracted light to beincident on an aperture 250 of an objective lens 50, and (e) is a plandiagram of a hemispherical surface illustrating a line-and-space patternallowing diffracted light to be incident on the apertures 204 and 250 ofthe objective lenses 50 and 60 in the case of performing verticalillumination.

FIG. 4 illustrates plan and side diagrams of a pattern chip according tothe first embodiment of the invention and an enlarged diagram of apattern portion.

FIG. 5A is a flowchart illustrating a flow of a process steps from S501to S515 for performing alignment of the wafer and the optical componentsaccording to the first embodiment.

FIG. 5B is a flowchart illustrating a flow of a process steps from S516to S528 for performing alignment of the wafer and the optical componentsaccording to the first embodiment.

FIG. 6 is a diagram illustrating a method of illumination alignmentaccording to the first embodiment, (a) is a diagram illustrating apattern image formed by scattered light which is generated from a wafer1 when the wafer 1 on which a line-and-space pattern is formed isirradiated with linearly-formed illumination light and incident on anobjective lens 40, and (b) is a partial enlarged diagram of (a), and (c)illustrates a waveform obtained by integrating an edge image of apattern image of (b) having a distribution which is the same as a lightintensity distribution of a thin-line illumination light irradiated onthe pattern image.

FIG. 7 is a diagram illustrating a method of sensor alignment accordingto the first embodiment, in which (a) is a plan diagram of an imagesensor illustrating a state where an image of scattered light generatedfrom a wafer is formed at positions shifted from centers of pixels onthe image sensor, and (b) is a plan diagram of the image sensorillustrating a state where an image of the scattered light generatedfrom the wafer is formed at a position coincident with centers of pixelson the image sensor.

FIG. 8 is a diagram illustrating an example of a sensor position qualitydetermination method, (a) is a graph illustrating a relationship betweena position of an image sensor 45 in an X direction perpendicular to anoptical axis of an objective lens 40 and a detection waveform when theimage sensor 45 detects the image of the pattern formed by the scatteredlight which is generated when the wafer 1 on which the line-and-spacepattern is formed is irradiated with the linearly-formed illuminationlight and incident on the objective lens 40, and (b) is a graphillustrating a relationship between a position of the image sensor 45 inthe optical axis direction of the objective lens 40 and a detectionwaveform when the image sensor 45 detects the image of the patternformed by the scattered light which is generated from the wafer 1 whenthe wafer 1 on which the line-and-space pattern is formed is irradiatedwith the linearly-formed illumination light and incident on theobjective lens 40.

FIG. 9 is a block diagram illustrating schematic configurations of adetection optical system and a focus detection system when an AF systemaccording to a second embodiment of the invention is configured as a TTLtype as seen from the front side.

(a) of FIG. 10 is plan and front diagrams of an image sensorillustrating a configuration for implementing a high accuracy of sensoralignment according to a third embodiment of the invention, (b) is agraph, as a comparative example of the third embodiment, illustrating arelationship between a position of the image sensor 45 in the Xdirection perpendicular to the optical axis of the objective lens 40 anda detection waveform in the case of not employing a slit plate when theimage sensor 45 detects the image of the pattern formed by the scatteredlight which is generated from the wafer 1 when the wafer 1 on which theline-and-space pattern is formed is irradiated with the linearly-formedillumination light and incident on the objective lens 40, and (c) is agraph, as a configuration of the third embodiment, illustrating arelationship between a position of the image sensor 45 in the Xdirection perpendicular to the optical axis of the objective lens 40 anda detection waveform in the case of not employing a slit plate when theimage sensor 45 detects the image of the pattern formed by the scatteredlight which is generated from the wafer 1 when the wafer 1 on which theline-and-space pattern is formed is irradiated with the linearly-formedillumination light and incident on the objective lens 40.

FIG. 11 is a block diagram illustrating a whole configuration of aninspection device according to a fourth embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the invention, in a defect inspection device including a plurality ofdetection optical systems, in order to cope with a phenomenon whereimages detected by the plurality of detection optical systems aredefocused due to a variation of a focal plane of a detection lens causedby a change in temperature or atmospheric pressure or due to a variationin offset of an off-axis focus details output system caused by a changein temperature and, thus, defect detection sensitivity is deteriorated,a focal plane of the detection lens and an offset value of auto-focusingare obtained, and a sensor of each of the detection optical systems isaligned with a conjugate image plane.

In order to improve an accuracy of the alignment of each sensor with animage plane and to reduce a time of alignment, a pattern chip formed sothat the same light amount is incident on each of apertures of theplurality of detection optical systems in a state where illuminationlight illuminating a wafer and a wafer plane are fixed is arranged nextto a chuck unit chucking the wafer.

Hereinafter, embodiments will be described with reference to thedrawings.

First Embodiment

In the embodiment, an example of a device of optically detecting adefect of a semiconductor wafer will be described.

FIG. 1A illustrates a schematic configuration of a defect inspectiondevice 1000 according to the embodiment. The defect inspection device1000 according to the embodiment is configured to include a stage unit100, an illumination optical system 200, a detection optical systemsection 300, an image processing unit 75, an operation system 80, and amechanical system control unit 85.

The stage unit 100 includes a Z stage 105 which is movable in a Z axisdirection and on which a wafer 1 as an inspect object is mounted, a θstage 110 which is rotatable about the Z axis and on which the Z stageis mounted, an X stage 115 which is movable in an X axis direction andon which the θ stage is mounted, and a Y stage 120 which is movable in aY axis direction and on which the X stage is mounted. A wafer chuck 101for holding the wafer 1 is installed in the Z stage 105.

The illumination optical system section 200 includes an obliqueillumination system 201 and a vertical illumination system 202.

The oblique illumination system 201 includes a laser light source 5, ashutter 7, an attenuator 8, a beam expander 9, plane mirrors 10 and 13,a ½-wavelength plate 16, a ¼-wavelength plate 20, a plane mirror 25, anda cylindrical condenser lens 30. The oblique illumination system expandsa diameter of a laser beam emitted from the laser light source 5 byusing the beam expander 9, adjusts a polarization state by passing thelaser beam through the ½-wavelength plate 16 and the ¼-wavelength plate20, shapes the laser beam in a one-direction-elongated shape by usingthe cylindrical condenser lens 30, and illuminates the wafer 1 held onthe Z stage 105 by the wafer chuck 101 with the laser beam in an obliquedirection.

On the other hand, the vertical illumination system 202 shares theconfiguration of from the laser light source 5 to the ¼-wavelength platewith the oblique illumination system 201 and is configured to furtherinclude a plane mirror 24 arranged to be taken in/out between the¼-wavelength plate 20 and the plane mirror 25, a plane mirror 26reflecting a laser beam reflected by the plane mirror 24, a cylindricalcondenser lens 27 shaping the laser beam reflected by the plane mirror26 in a one-direction-elongated shape, and a reflection mirror 28reflecting the laser beam shaped in the one-direction-elongated shape bythe cylindrical condenser lens 27 and irradiating the wafer 1 in adirection vertical to the wafer.

The plane mirror 24 can be taken in/out on an optical path of the laserbeam directing from the ¼-wavelength plate 20 toward the plane mirror 25to reflect the laser beam upwards, and the plane mirror 26 reflects thelaser beam of which optical path is bent upwards by the plane mirror 24in the direction parallel to the upper surface of the wafer 1. Thecylindrical condenser lens 27 shapes the laser beam reflected by theplane mirror 26 in the one-direction-elongated shape, and the reflectionmirror 28 is arranged on the optical axis of the objective lens 40 ofthe detection optical system section 300 to reflect the laser beamshaped in the one-direction-elongated shape by the cylindrical condenserlens 27 and irradiates the same point as the point on the wafer 1 whichis irradiated with linearly-formed illumination light 35 by the obliqueillumination system 201 from the direction vertical to the surface ofthe wafer 1 along the optical axis of the objective lens 40.

The detection optical system section 300 is configured to includeobjective lenses 40, 50, and 60, imaging lens systems 41, 51, and 61which form images of scattered light from the surface of the wafer 1collected by the respective objective lenses, image sensors 45, 55, and65 which detect optical images formed by the respective imaging lenses,optical-axis-direction driving mechanisms 47, 57, and 67 which drive therespective image sensors in the optical axis directions of thecorresponding objective lenses, and vertical-to-optical-axis directiondriving mechanisms 49, 59, and 69 which drive the respective imagesensors in the directions perpendicular to the optical axes of thecorresponding objective lenses, so that the scattered light from thewafer 1 which is irradiated with the laser beam shaped in aone-direction-elongated shape is collected by the objective lenses 40,50, and 60, and the images formed by the imaging lens systems 41, 51,and 61 are detected by the image sensors 45, 55, and 65 respectively.

In addition, the defect inspection device 1000 includes a lightillumination unit 131 and a light-receiving portion 135 as a heightdetection unit (AF system) 130 for autofocusing for detecting the heightof the surface of the wafer 1 mounted on the Z stage 105.

According to the configuration described above, with respect to theinspection object wafer 1 held by the wafer chuck 101, the wafer 1 isirradiated with the laser which is emitted from the laser light source 5and is shaped in a one-direction-elongated shape by the cylindricalcondenser lens 30 as the thin-line illumination light 35 in the obliquedirection. The thin-line illumination light 35 irradiated on the wafer 1is shaped so that the elongated direction becomes the Y direction andthe light is allowed to converge to be thinned in the X direction wherethe wafer 1 is scanned at a constant speed. The line width in the Xdirection is thinned to be about 0.5 to 2.0 μm.

As illustrated in FIG. 1A, the illumination optical system section 200is configured with the components of from the laser light source 5 tothe cylindrical condenser lens 30. As a candidate of the laser emittedfrom the laser light source 5, there are 355 nm in a UV (ultraviolet)range, 266 nm and 213 nm in a DUV (deep UV) range, 199 nm, 193 nm, andthe like. In addition, illumination by laser including a plurality ofwavelengths among the above wavelengths may be considered.

Transmitting and blocking of the laser beam oscillated from the laserlight source 5 is controlled by the shutter 7 to be incident on theattenuator 8, so that the transmitted light amount is adjusted. In orderto irradiate the wafer 1 with the thin-line illumination light 35 whichis shaped in a desired shape, a beam diameter is shaped by the beamexpander 9, and the optical path is bent by the plane mirrors 10 and 13.The plane mirrors 10 and 13 are provided with respective mechanisms 10′and 13′ moving the laser beam toward the incident directions (directionsindicated by arrows 11 and 14) and respective tilt mechanisms 10″ and13″ adjusting angles of reflected light in incident planes (directionsindicated by arrows 12 and 15), so that the plane mirrors have afunction of correcting the position and angle of the laser beams emittedfrom the laser light source 5. In addition, in order to controlpolarization of the illumination light, the ½-wavelength plate 16 andthe ¼-wavelength plate 20 are provided with respective rotationmechanisms 16′ and 20′ independently performing rotation in thedirections of the arrows 17 and 22. As an example of the polarization inthe wafer 1, S-polarization, P-polarization, linear polarization(intermediate polarization between the S-polarization and theP-polarization) vibrating in the direction of the pattern pitch formedon the wafer 1, and arbitrary elliptic polarization are considered.

The plane mirror 25 reflects the laser beam passed through the¼-wavelength plate 20 toward the wafer 1 side, and incident in thecylindrical condenser lens 30 to form the thin-line illumination 35 onthe wafer 1. In the area of the wafer 1 which is irradiated with thethin-line illumination light 35, by using the plane mirror 25 and thecylindrical condenser lens 30 as an integral component, the illuminationposition in the X direction can be adjusted by the X direction shiftmechanism 25′ performing shift in the incident direction (directionindicated by an arrow 27) of the laser beam on the plane mirror 25. Inaddition, in order to adjust the focus of the thin-line illuminationlight 35 which is irradiated on the wafer 1, included is also a focusadjustment mechanism 30′ shifting the cylindrical condenser lens 30 inthe optical axis direction (direction indicated by an arrow 32) of thethin-line illumination light 35.

Among the scattered light generated from the area of the wafer 1 whichis irradiated with the thin-line illumination light 35, the scatteredlight scattered in the directions of the three objective lenses 40, 50,and 60 is captured by the three objective lenses 40, 50, and 60, andthus, the optical images are formed on the image sensors 45, 55, and 65by the imaging lens systems 41, 51, and 61, so that the optical imagesare detected by the image sensors 45, 55, and 65. As the image sensor,there are a line sensor where CCDs (charge coupled devices) are arrayedin a line shape, a TDI (time delay integration) type sensor, and a CMOS(complementary metal oxide semiconductor) type image sensor. The imagesensors are provided with at-least-two-axis-position adjustmentmechanisms (optical-axis-direction driving mechanisms 47, 57, and 67 andvertical-to-optical-axis direction driving mechanisms 49, 59, and 69) sothat the illumination area of the thin-line illumination light 35 on thewafer 1 and the light-receiving planes of the image sensors 45, 55, and65 have conjugate relations.

In the example of the image sensor 45, the position alignment of thelight-receiving plane of the image sensor 45 with the focused imageplane is performed by the optical-axis-direction driving mechanism 47which moves in the optical axis direction. In addition, the lightincident on the lens 40 among the scattered light scattered from thearea of the wafer 1 which is irradiated with the thin-line illuminationlight 35 is focused in a linear shape on the image plane by the imaginglens system 41. The image sensor 45 is positioned in the width directionby the vertical-to-optical-axis direction driving mechanism 49 which isa mechanism of moving the image sensor 45 in the width direction so thatthe center of the linearly-shaped optical image in the width directionand the center of the light-receiving portion of the image sensor 45 inthe width direction are coincident with each other. Similarly, withrespect to the image sensor 55, the image sensor is positioned by theoptical-axis-direction driving mechanism 57 moving the image sensor inthe optical axis direction and the vertical-to-optical-axis directiondriving mechanism 59 moving the image sensor in the width direction ofthe image sensor 55, and with respect to the image sensor 65, the imagesensor is positioned by the optical-axis-direction driving mechanism 67moving the image sensor in the optical axis direction and thevertical-to-optical-axis direction driving mechanism 69 moving the imagesensor in the width direction of the image sensor 65.

The three image data simultaneously detected by the image sensors 45,55, and 65 are transmitted to the image processing unit 75. The imageprocessing unit 75 performs position alignment with an adjacent dieimage, a reference image, or the like to calculate a differential imageor to calculate feature amounts of the images. By comparing thesedifferential image data or feature amounts with predefined thresholdvalues, defects are determined. These data are transmitted to theoperation system 80, and the feature amounts such as a map, coordinates,and sizes of the detected defects can be displayed through a GUI(graphical user interface) (not shown).

The operation system 80 is configured to be connected to an upper levelsystem so that the operation system can be, for example, instructed toperform the inspection or instructed to perform retrieving/displaying ofprevious inspection data, setting-up of an inspection recipe, and thelike through the upper level system. For example, in a case where theoperation system 80 is instructed to perform the inspection, the drivingunits are operated in the order of inspection sequence through themechanical system control unit 85.

The operation steps of the inspection sequence are as follows asillustrated in FIG. 1B.

The optical components are set so as to be in the optical conditionsregistered in the inspection recipe (S101).

The pattern chip 150 arranged next to the chuck is moved to a commonobject point of the objective lenses 40, 50, and 60 (S102).

The pattern chip 150 is irradiated with the thin-line illumination light35, and the height of the surface of the pattern chip 150 is aligned(S103).

The diffracted light from the area which is irradiated with thethin-line illumination light 35 is captured by the objective lenses 40,50, and 60, and the image sensors are positioned by the movingmechanisms 47, 49, 57, 59, 67, and 69 of the image sensors so that thewidth center of the area which is irradiated with the thin-lineillumination light 35 and the centers of width (width of one pixel inthe direction perpendicular to the row of pixels: width of onecorresponding pixel in the wafer scan direction) of the image sensors45, 55, and 65 are coincident with each other (S104).

The inspection object wafer 1 is loaded, and the wafer 1 is suctioned tothe chuck 130 (S105).

In the X stage 115, the Y stage 120, and the θ stage 110, the alignmentof the X, Y, and θ (rotation) of the wafer 1 are performed (S106).

The wafer 1 is positioned at the inspection start position, and whilemoving at a constant speed in the X direction, the image is continuouslyacquired by the image sensors 45, 55, and 65 (S107). At this time, theheight of the surface of the wafer 1 is measured by the off-axis AF(Auto Focus) system 130 including a light-emitting unit 131 and alight-receiving unit 135, and in a case where the focus position and ashift of the height exceeds an allowable range, height alignment isperformed in the Z stage 105.

In a case where the field of view reaches the end of the inspectionobject area, the Y stage 120 is stepwise-moved, and while scanning the Xstage 115 at a constant speed, the image is acquired again. Until allthe images of the inspection object area are detected, this operation isrepetitively performed (S108).

In the case of performing the inspection by using the configurationdescribed above, as disclosed in “PROBLEM TO BE SOLVED BY THEINVENTION”, the focus positions of the imaging lens systems 41, 51, and61 including the objective lens 40, 50, and 60 are changed. If thisproblem is not solved, the defocused images are detected by the imagesensors 45, 55, and 65, and thus, the inspection sensitivity isdeteriorated. In addition, in the case of performing the inspection byusing a plurality of devices of the same type, a device variation, thatis, a difference in inspection sensitivity among the devices may occur.Therefore, in S104, the correction of the focus positions or the like ofthe imaging lens systems 41, 51, and 61 including the objective lenses40, 50, and 60 needs to be performed at a high accuracy.

The process of performing the correction is illustrated in FIG. 2. Inaddition, in FIG. 2, for simplifying the description, the imaging lenses41, 51, and 61 are omitted in illustration, and it is described that theimage of the scattered light from the wafer 1 is formed by the objectivelenses 40, 50, and 60. As an example, the focus positions of theobjective lenses 40, 50, and 60 are coincident in the pattern chipsurface 151. At this time, the peripheral light beams (indicated bybroken lines) are denoted by 43, 53, and 63. The point where theseperipheral light beams intersect on the image plane is an image point,and the center of the image sensors 45, 55, and 65 are arranged at thecenters of the image point.

However, due to a variation of temperature, atmospheric pressure, or thelike, the focus position (object position) of the objective lens 40 ischanged to the position of the lower pattern chip surface 151′. At thistime, the peripheral light beams (indicated by solid lines) are changedas 43′, 53′, and 63′. In this case, the positions of the image sensors45, 55, and 65 are defocused from the image point.

Therefore, as illustrated in FIG. 1C, in step S104, the positions of theimage sensors are aligned with the image point in the following detailedsteps.

The surface height of the pattern chip 150 is stepwise-moved, the imageof the image plane observation camera 171 fixedly arranged at the designposition of the image plane is detected, contrast or brightness of thedetected pattern image is calculated, and the height where the height ofthe focal plane of the objective lens 40 is coincident with the heightof the surface height of the pattern chip 150 is sensed (S1041).

The surface of the pattern chip 150 is positioned at this position, thedetection value output from the light-receiving portion 135 of the AFsystem 130 is stored, and the AF detection value of this case is definedas a reference of the focal plane (S1042). By irradiating the wafer 1with the thin-line illumination light 35 so that the illumination widthis maximally reduced (so that the focus position of the thin-lineillumination light 35 is aligned on the surface of the pattern chip 150)in the state where the surface of the pattern chip 150 is positioned onthe focal plane, the illumination focus adjustment is performed whiledetecting the image of the image plane observation camera 171 (S1043).

Next, the positions of the image sensors 40, 50, and 60 are aligned withthe positions 45′, 55′, and 65′ on the image plane of the peripherallight beams 43′, 53′, and 63′ connecting the object points of theobjective lenses 40, 50, and 60 and the image points of the imaginglenses 41, 51, and 61 (refer to FIG. 1, omitted in illustration in FIG.2) (S1044).

In this case, the position alignment is performed by theoptical-axis-direction driving mechanisms 47, 57, and 67 which aremoving mechanisms in the optical axis directions Z, Z′, and Z″ describedwith reference to FIG. 1 and the vertical-to-optical-axis directiondriving mechanisms 49, 59, and 69 which are moving mechanisms in thesensor width directions X, X′, and X.

With respect to the problem of performing the operations describedabove, in order to accurately, speedily sense appropriate positions 45′,55′, and 65′ of the image sensors 45, 55, and 65, diffracted light orreflected light from the pattern chip 150 needs to be simultaneouslydetected.

In the width direction of the thin-line illumination light, preferably,a luminance distribution of the detection image corresponds to anillumination luminance distribution. If a diffusion surface such as asatin finished surface is irradiated with the thin-line illuminationlight, since the intensities of reflected light and scattered light arechanged according to the uneven state at the position which isirradiated with the illumination light, in order to avoid the problem ofan increase of an calculation error of the center or the width in thewidth direction of the illumination light irradiated on the wafer 1, theabove configuration is needed.

As a method satisfying the above two points, considered is a method ofusing a plurality of pattern groups of which directions ofline-and-space patterns are different so that diffracted light isincident on apertures of detection systems according to illuminationazimuth and elevation angles.

FIG. 3 illustrates apertures of illumination and detection systems anddirections of line-and-space patterns for allowing diffracted light tobe incident on the apertures. (a) of FIG. 3 illustrates an upperhemisphere 173 of a surface of the wafer 1. The state illustrated inFIG. 3(a) is an example of a state where illumination light isirradiated on the wafer 1 through a point 170 of the hemisphere 173 bythe oblique illumination system 201 and specular reflection light fromthe wafer 1 reaches a point 175 of the hemisphere. The azimuth angle andthe elevation angle formed by the illumination light of the obliqueillumination system 201 and the Y axis are set to 180 and 185,respectively. The diagrams of the hemisphere as seen from the topthereof (top view of the hemisphere 173) are illustrated in (b) to (e)of FIG. 3. An outer circumferential portion 178 corresponds to NA 1.

(b) of FIG. 3 illustrates the direction of a line-and-space pattern 205which allows the diffracted light to be incident on the aperture 204 ofthe objective lens 60 of FIG. 2. The specular reflection light from thewafer 1 caused by the illumination light which is irradiated on thewafer 1 through the point 170 on the hemisphere 173 by the obliqueillumination system 201 reaches the point 175 on the hemisphere 173. Thepoint 175 on the hemisphere 173 becomes a position having a pointsymmetry with the point 170 with respect to the center 179 of thehemisphere 173. In case the line-and-space pattern 205 is formed in thedirection perpendicular to a line 190 connecting the position 175 whichthe specular reflection light reaches and the center of the aperture 204of the objective lens 60 on the plan diagram of the hemisphere 173, thediffracted light from the wafer 1 is incident on the aperture 204 of theobjective lens 60. In addition, with respect to a pitch of theline-and-space pattern 205, a pitch of incidence on the aperture 204 maybe calculated from the angle (three-dimensional angle) between the point175 which the specular reflection light reaches and the aperture 204 onthe hemisphere 173.

Similarly, (c) of FIG. 3 illustrates an example of the aperture 210 ofthe objective lens 40 in a case where the detection system is arrangedin the direction normal to the wafer 1 (the case corresponding to theobjective lens 40 of FIG. 2). A line-and-space pattern 230 is formed inthe direction perpendicular to a line 220 connecting the point 175 onthe hemisphere 173 which the specular reflection light generated fromthe wafer 1 by the illumination light which is irradiated on the wafer 1through the point 170 on the hemisphere 173 reaches and the center ofthe aperture 210 of the objective lens 40. In addition, (d) of FIG. 3illustrates an example of a line-and-space pattern 245 which allows thediffracted light from the wafer 1 to be incident on the aperture 250 ofthe objective lens 50 in FIG. 2. A line-and-space pattern 245 is formedin the direction perpendicular to a line 240 connecting the specularreflection light 175 and the center of the aperture.

In addition, (e) of FIG. 3 illustrates an example of a case where theillumination light is illuminated on the wafer 1 in the verticaldirection by the vertical illumination system 202. In the case of thevertical illumination system 202, the point indicating the illuminationlight and the specular reflection light is denoted by 171. In thevertical illumination, the straight line connecting the specularreflection light 171 and the center of the aperture center is parallelto the X axis, and the line-and-space pattern formed in the directionperpendicular thereto is parallel to the Y axis. In this case, accordingto which position of a Gauss distribution in an illumination widthdirection the edge portion of the line-and-space pattern is arranged at,the intensity detected by the image sensor is changed, and thus, theerror of calculation of the center or the width in the illuminationwidth is increased. In order to avoid this problem, in the embodiment,the pattern is formed in a direction 260 perpendicular to a straightline 255 connecting a position in an aperture shifted from the centersof apertures 204 and 250 and a specular reflection light 171.

An example of the pattern chip for performing the position alignment ofthe image sensors 40, 50, and 60 arranged in the plurality of detectionsystems of the detection optical system section 300 in the plurality ofillumination conditions (oblique illumination/epi-illumination (verticalillumination)) is illustrated in FIG. 4. In the pattern chip 150,patterns are formed on a surface 270 (refer to (b) of FIG. 4) of a glasssubstrate, N periods of the patterns are formed in units of a block Aformed in the area 275 (refer to FIG. 4). As illustrated in the enlargeddiagram of FIG. 4, three patterns for oblique illumination and onepattern for epi-illumination are formed in the block A.

The formed patterns for oblique illumination are the line-and-spacepattern 205 for the aperture 204, the line-and-space pattern 230 for theaperture 210, and the line-and-space pattern 245 for the aperture 250illustrated in FIG. 3(b). In addition, the line-and-space pattern 260which is used for the apertures 204 and 250 during the verticalillumination by the vertical illumination system 202 is formed. Thewidth of the block A provided with the patterns in four directions whereorientations (oblique angles of the patterns) in the elongateddirections of the line-and-space patterns are different from each otheraccording to the arrangement (azimuth angles and elevation angles withrespect to the positions on the pattern chip 150 irradiated with thelinearly-formed illumination light 35) are about several micrometers toseveral hundreds of micrometers. As a pattern material, a metal film ofCr, Al, or the like or a pattern of SiO₂ formed by etching isconsidered.

As illustrated in FIG. 1, the pattern chip 150 is arranged next to thechuck 101 on the Z stage 105. For example, in a case where theinspection is performed with the illumination conditions being changedfrom the illumination by the oblique illumination system 201 to theepi-illumination by the vertical illumination system 202, after setting(inserting the plane mirror 24 into the optical path of the later beambetween the ¼-wavelength plate 20 and the plane mirror 25 to bent theoptical path of the laser beam passing through the ¼-wavelength plate 20toward the direction of the plane mirror 26) of components in theoptical conditions of the vertical illumination, the focus andhorizontal position of the illumination light by the verticalillumination system 202 and the optical-axis-direction positions(focuses) and the inside-image-plane positions of the plurality of imagesensors 45, 55, and 65 of the detection optical systems 300 can bealigned with the wafer 1 by the pattern chip 150.

By doing so, in parallel with a θ pre-alignment operation performed byloading the inspection object wafer by a mini-environment system andcontrolling the θ stage 110, the alignment of the position of theillumination light by the vertical illumination system 202 irradiated onthe wafer 1 with the positions of the image sensors 45, 55, and 65 ofthe detection optical system 300 can be performed, so that it ispossible to obtain the effect of improvement of the throughput of theinspection device.

With respect to the timing of performing the alignment of the positionof the illumination light by the vertical illumination system 202irradiated on the wafer 1 with the positions of the image sensors 45,55, and 65 of the detection optical systems 300, considered are a timewhen the illumination condition or the detection condition is changedfrom the previous inspection conditions, a time when the mechanism unitof the device is returned to the origin point, a time when thetemperature or atmospheric pressure in the device is varied to be apredetermined value or more, a time when the alignment is periodicallyperformed according to a predefined time, and the like. The flow of thealignment of the position of the illumination light by the verticalillumination system 202 irradiated on the wafer 1 with the positions ofthe image sensors 45, 55, and 65 of the detection optical systems 300 isillustrated in FIGS. 5A and 5B.

First, on a GUI screen (not shown) of the operation system 80, byselecting an inspection recipe where an illumination condition, a waferAF value, a detection condition when the wafer 1 is detected, thethreshold value information for determination of defects in the imagingprocess, and the like are registered, and inspection start is commanded.At the inspection start, first, the previous inspection conditions arechecked, and next, the time elapsed after the performing of the previousalignment operation is checked. And then, it is checked whether or notthe currently performing inspection is lot inspection.

The next steps are as follows.

Preparation Operations Before Position Alignment

-   -   1) Start wafer, illumination and sensor alignment (S501).    -   2) Set illumination conditions (S502).    -   3) Set detection conditions (S503).    -   4) Move the pattern chip in the field of view of the detection        system (S504).    -   5) Set Auto Focus (AF) ON (S505).

Surface Alignment of Wafer

-   -   6) Move the observation camera of the detection (2) to the        center of the field of view (S506).    -   7) Stepwise move the height of the pattern chip (S507).    -   8) Calculate the contrast of the detection image of the        observation camera (S508).    -   9) Determine focusing by comparing the calculated contrast with        a predetermined focusing contrast determination range (S509).    -   In a case where “out of focus” is determined, the procedure        proceeds to 7).    -   In a case where “in focus” is determined, the procedure proceeds        to 10).    -   10) Read and update the AF value in the state where the surface        of the pattern chip is in focus (S510).    -   11) Complete the alignment of the height of the pattern chip        (S511).

Alignment of Illumination

-   -   12) Move all the driving systems to previous setting values of        the same illumination conditions (S512).    -   13) Stepwise move of the thin-line illumination along the focus        axis (S513).    -   14) Determine whether the illumination focus is in or out of an        allowable range in the detection by the image plane observation        camera (S514).    -   In a case where it is determined that the focus is out of the        allowable range, 15) perform the stepwise movement to the focus        side (S515).    -   In a case where it is determined that the focus is in the        allowable range, complete the focus alignment.    -   16) Calculate X-direction shift of the illumination center from        the image which is determined to be in focus in step 14) (S516).    -   17) Move the X direction to the target position (S517).    -   18) Perform image detection and determine whether the position        is in or out of the X direction allowable range (S518).    -   In a case where it is determined that the X position is out of        the allowable range, the procedure proceeds to 17).    -   In a case where it is determined that the X position is in the        allowable range, 19) complete the alignment of the illumination        (S519)

Alignment of Linear Sensor (the Same Alignment being Performed on ThreeDetection Systems)

-   -   20) Perform stepwise movement in the X direction (S520).    -   21) Determine whether the center shift between the illumination        center and the sensor center is in or out of an allowable range        (S521).    -   In a case where it is determined that the center shift is out of        the allowable range, 22) determine the direction where the        illumination center and the sensor center are coincident (S522).    -   23) Perform X stepwise movement of the sensor in the direction        where the centers are coincident (S523).

The process proceeds to 21).

-   -   In a case where it is determined that the center shift is out of        the allowable range, the process proceeds to 24).    -   24) Perform stepwise movement of the linear sensor in the focus        Z direction (S524).    -   25) Determine whether the focus is in or out of an allowable        range (S525).    -   In a case where it is determined that the focus is out of the        allowable range, 26) determine the focus direction (S526).    -   27) Perform stepwise movement to the focus side (S527).    -   25) The procedure proceeds to 25).    -   In a case where it is determined that the focus is out of the        allowable range, 28) complete the linear sensor alignment        (S528).

In addition, in a case where the oblique illumination and the verticalillumination are simultaneously performed, the illumination alignmentsteps (S512) to (S519) may be performed for each of the obliqueillumination and the vertical illumination.

Among the position alignment steps for wafer/illumination/detectionsystem image sensors, the examples of determining whether to be in orout of the allowable range are illustrated in FIGS. 6 to 8.

An X direction position determination method for a thin-lineillumination is illustrated in FIG. 6. (a) is an example of an imageobtained by irradiating the pattern chip 150 with the thin-lineillumination light 35 in the oblique direction in the state where thepattern chip 150 is moved to the position intersecting the optical axisof the objective lens 40, reflecting the pattern image formed withcomponents incident on the objective lens 40 among the reflected andscattered light generated from the area on the pattern chip 150 which isirradiated with the thin-line illumination light 35 by using areflecting mirror 180 arranged in front of the image sensor 45 on theoptical axis of the objective lens 40 as illustrated in FIG. 2, anddetecting the reflected pattern image by the image plane observationcamera 171. During the imaging of the pattern image, the height of thesurface of the pattern chip 150 is detected by a height detection unit(AF system) 130 for autofocusing, and the Z stage 105 is controlled bythe mechanical system control unit 85, so that the height of the surfaceof the pattern chip 150 is maintained constant.

According to the arrangement of the objective lens 40, in a case wherethe thin-line illumination light 35 is irradiated in the obliquedirection, in the block A formed in the pattern chip 150 illustrated inthe enlarged diagram of FIG. 4, a plurality of edge images 300 (whitepoints of FIG. 6(a)) formed by allowing the diffracted light generatedfrom the edge portions of the line-and-space pattern 230 formed in thearea of the pattern b and incident on the aperture 210 of the objectivelens 40 are clearly detected corresponding to the pattern period of theline-and-space pattern 23. Since no diffracted light is formed from thelight incident on the aperture 210 of the objective lens 40 among thediffracted light generated from the line-and-space patterns 205, 245,and 260 formed in the other pattern areas a, c, and d on the patternchip 150, dark images are formed.

The enlarged image of a portion of the edge image 300 generated by theline-and-space pattern 23 formed in the area of the pattern b isillustrated in FIG. 6(b). A waveform 310 obtained by integrating theedge image 300, which are periodically detected, in the Y direction isillustrated in FIG. 6(c). The waveform 310 has a distribution which isthe same as a light intensity distribution of the thin-line illuminationlight 35 irradiated on the line-and-space pattern 23 formed in the areaof the pattern b of the pattern chip 150, and the distribution isideally a Gauss distribution. The center of the waveform 310 iscalculated. As an example of a method for the calculation, there areGauss fitting, calculation of a central value of two points intersecting50% of a brightness maximum value and the waveform 310, and calculationof the brightness maximum value, and the like.

In this manner, the center of the waveform 310 of the edge image 300detected by the image plane observation camera 171 is obtained, thedifference to a predefined X-direction target position 330 of thethin-line illumination light 35 is calculated, the illumination area onthe wafer 1 by the thin-line illumination light 35 is moved in the Xdirection by the X direction shift mechanism 25′ so that the differenceis included within a predefined allowable range.

Next, the position where the focus position of the thin-lineillumination light 35 is coincident with the surface of the pattern chip150 is a position where a width (for example, a full width at halfmaximum or a 1/e² width) of the detected waveform 310 becomes in minimumor a position where the brightness maximum value of the waveform 310 isin maximum, and these values are used as evaluation values. Theadjustment of the focus position of the thin-line illumination light 35is performed so that the focus position is included in the allowablerange by repetitively performing the operations of setting the allowablerange, performing the stepwise movement of the thin-line illuminationlight 35 by the focus alignment mechanism 30′, performing the imagedetection, and performing calculation of the evaluation value,determining whether to be in or out of the allowable range.

FIG. 7 illustrates a method of alignment of the image sensors 45, 55,and 65 arranged in the respective detection systems. Since any one ofthe image sensors performs the same alignment operation, the alignmentof the image sensor 45 is representatively described. FIG. 7(a)illustrates a schematic diagram of a light-receiving portion 365 of theimage sensor 45. In the image sensor 45, a plurality of pixels 365′ arearranged in one column in the Y direction, and the center of the pixelwidth in the X direction is denoted by 360. A detection image obtainedby allowing the image sensor 45 to detect the image formed by thescattered light generated from the pattern chip 150 irradiated with thethin-line illumination light 35 is denoted by 35′, and the edge image300 formed by the scattered light from the line-and-space pattern 230formed in the area of the pattern b of the pattern chip 150 is detectedto be bright. The X direction alignment is performed by allowing thecenter position 350 of the edge image 300 in the X direction projectedon the image sensor 45 and the center position 360 of the image sensorin the width direction to be coincident with each other. If there is ashift amount ΔX, the pattern image 300 exceeds the light-receivingportion 365 of the image sensor 45, so that the detected waveform 301 ofthe image sensor 45 is in the state where the brightness is low.

On the other hand, as illustrated in FIG. 7(b), in the state where thecenter position 350 of the edge image 300 in the X direction and thecenter position 360 of the image sensor in the width direction arecoincident with each other, the brightness of the waveform 302 becomesin maximum. There is an object to allow the X direction of the imagesensor 45 to be coincident in this state by the vertical-to-optical-axisdirection driving mechanism 49.

A relationship between the position of the image sensor 45 in the Xdirection and the brightness of the detected waveform is illustrated inFIG. 8(a). In FIG. 8(a), the “brightness S” of the vertical axis is, forexample, a maximum value of the edge image 300 or an average value ofthe maximum values obtained from a plurality of edge images 300. In thestate where the center of the pixel width of the image sensor 45 (referto FIGS. 7(a) and 7(b)) and the center of the edge image 300 arecoincident with each other, the brightness S becomes in maximum, and inthe state where the position of the edge image 300 in the X direction isincluded in the width direction (pixel width in FIGS. 7(a) and 7(b)) ofthe rectangular pixel 365′ of the image sensor 45, the brightnessbecomes high. Therefore, while performing the stepwise movement of thevertical-to-optical-axis direction driving mechanism 49, the brightnessS is calculated from the output of each pixel 365′ of the image sensor45. Sth obtained by multiplying a threshold value K₁ and the maximumvalue Smax is used as a threshold value, and sensor positions X370 and375 of the brightness S intersecting the threshold value Sth arecalculated. The center 360 of the two points is used as the positionwhere the center of the pixel width of the image sensor 45 and thecenter of the edge image 300 (=the center of the area on the patternchip 150 illuminated with the thin-line illumination light 35) arecoincident with each other, and the position of the image sensor 45 isdetermined by the vertical-to-optical-axis direction driving mechanism49.

In order to focus the edge image 300 on the surface of the pattern chip150, as illustrated in FIG. 8(b), the image sensor 45 is stepwise movedin the optical axis direction by the optical axis direction movingmechanism 47, and the brightness S detected by the image sensor 45 ateach position is obtained. The horizontal axis denotes the moving amountof the image sensor 45 in the optical axis direction (optical axisdirection of the imaging lens 41: Z direction) by theoptical-axis-direction driving mechanism 47, and the vertical axisdenotes the brightness S as the output of the image sensor 45. While theimage sensor 45 is stepwise moved by the optical-axis-direction drivingmechanism 47, the brightness S (381, 382, and 383) detected by the imagesensor 45 is calculated. A quadratic curve 385 is obtained by performingsecond-order approximation at a plurality of points (in this example,three points) including the maximum of the brightness, and the positionwhich is in maximum is determined as a target position of theoptical-axis-direction driving mechanism 47 for the image sensor 45.

According to the embodiment, the position alignment forwafer/illumination/detection system image sensors can be performed at agood accuracy, so that it is possible to maintain a high reliability ofthe result of the defect inspection.

Second Embodiment

As a second embodiment, a configuration example of replacing the AFsystem detecting a shift of the focus position of the objective lenswith respect to the surface of the wafer 1 by an off-axis-type AF systemdescribed in the first embodiment and configured as a TTL (through thelens) type will be described with reference to FIG. 9. Among componentsillustrated in FIG. 9, components having the same functions as those ofthe components denoted by the same reference numerals illustrated inFIG. 1 described above are omitted in description. In the configurationof the inspection device according to the first embodiment describedwith reference to FIG. 1, the configuration employing three detectionsystems as the detection optical system. However, in the configurationof the inspection device according to the embodiment illustrated in FIG.9, the configuration of two detection systems is employed, and thedescription thereof is omitted. The detection optical system accordingto the embodiment may be configured to include three detection systemslike the detection optical system according to the first embodimentdescribed with reference to FIG. 1 or three or more detection systems.

A TTL-type AF system 400 according to the embodiment is configured toinclude a light source 401 emitting light for AF, a cylindrical surfacelens 430 allowing the light for AF emitted from the light source 401 toconverge in one direction to form linearly-shaped light, a slit 450shaping the illumination light emitted from the cylindrical surface lens430 into slit light, a half mirror 455 reflecting the illumination lightpassing through the slit 450, a dichroic mirror 465 which is arranged soas to reflect the illumination light reflected by the half mirror 455toward the side of the objective lens 40 on the optical axis of theobjective lens 40 and reflects only the light in the wavelength range ofthe illumination light and transmits the laser beam for inspection, anda sensor 468 for AF which detects the reflected light from the surfaceof the wafer 1 which is reflected by the dichroic mirror 465, passesthrough the objective lens 40, is irradiated on the surface of theinspection object wafer 1, is reflected on the surface of the wafer 1,passes through the objective lens 40 again, is reflected by the dichroicmirror 465, and passes through the half mirror 455.

The pattern chip 150 is set to the position where the focus of thepattern image is aligned in the image plane observation camera 171. Theheight of the position is sensed by the AF detection system 400. Thelight source 401 for AF is a light source which emits light having awavelength different from the wavelength of the laser beam emitted fromthe laser light source 5 for inspection. AF light 420 is guided alongthe optical axis 410 of the AF system to illuminate the slit 450 throughthe cylindrical surface lens 430. In this case, the optical axis of theobjective lens 40 and the optical axis 410 of the AF system are shiftedby a shift amount 440, and the AF light is designed to be incident onthe slit 450 and the inspection object wafer 1 in the oblique direction.The slit 450 has an aperture which is thin in the X direction andelongated in the Y direction. AF light 460 passing through the slit 450is reflected by the half mirror 455, is reflected by the dichroic mirror465, is incident on the wafer 1 through the objective lens 40, and isreflected by the wafer 1. The reflected AF light is reflected by thedichroic mirror 465 through the objective lens 40 again and passesthrough the half mirror 455 to reach the sensor 468 for AF. As acandidate for the sensor 468 for AF, there are a one-dimensional CCDsensor or PSD (position sensitive detector) and a split-type photodiode.

If the height of the wafer 1 is varied, the position of incidence of theAF light, which is incident on the wafer 1 in the oblique direction, onthe surface of the wafer 1 is varied, and the reflected light from thesurface of the wafer 1 on which the position of incidence is varied isshifted at the position of the sensor 468 for AF in the width directionof the slit. The shift amount of the AF light is sensed, and a defocusamount is obtained from a relationship between the shift amount and thedefocus amount of the AF light which are geometrically obtained. The Zstage 105 is controlled based on the obtained defocus amount by themechanical system control unit 85 to perform the focus alignment.

In addition, in a case where the focus position of the objective lens 50is shifted from a position 498 according to the variation in temperatureand atmospheric pressure, the position which is irradiated with thethin-line illumination light 35 needs to be corrected to a position 495.Since the sensor position needs to be aligned from a before-shiftposition 65 to a position 65′, the correction is performed by using theoptical-axis-direction driving mechanism 67 and thevertical-to-optical-axis direction driving mechanism 69.

Third Embodiment

In the embodiment, an example where the vertical-to-optical-axisdirection alignment of the image sensors 45, 55, and 65 described in thefirst embodiment is performed at a higher accuracy is illustrated inFIG. 10(a). Herein, although the image sensor 45 is representativelydescribed, the image sensors 55 and 65 also perform the same operations.A basic whole configuration of a defect inspection device according tothe embodiment is the same as that of FIG. 1, and thus, herein,peripheral configurations of the image sensors 45, 55, and 65 aredescribed.

In the first embodiment, since the width of the image sensor 45 is widerthan the image width of the illumination light when the thin-lineillumination light 35 is irradiated on the wafer 1 on which theline-and-space pattern is formed, as illustrated in FIG. 10(b), evenwhen the image sensor 45 is moved in the direction (X direction)perpendicular to the optical axis, there occurs the area 490 where thesensor output is not changed in the state where the detected brightnessis high. In this case, the image sensor 45 is driven up to the positionwhere the image by the scattered light incident on the objective lens 40among the diffracted light from the area on the wafer 1 which isirradiated with the thin-line illumination light 35 is deviated from thelight-receiving portion of the image sensor 45, and from the positionwhere the light amount is reduced, the center of the area which isilluminated with the thin-line illumination light 35 and the widthcenter of the image sensor 45 are allowed to be coincident with eachother.

In the embodiment, as illustrated in FIG. 10(c), without the area 490,by increasing the amount of change of the brightness with respect to themovement in the X direction of the sensor, the center alignment isperformed at a high accuracy. The configuration of the image sensor 45according to the embodiment is illustrated in FIG. 10(a). Only at thetime of adjusting the vertical-to-optical-axis direction (X direction)position of the image sensor 45, the slit 480 of the slit plate 475 isarranged just in front of the image sensor 45. The width of the slit 480of the slit plate 475 is thinner than the image of the thin-lineillumination 35 which is projected on the image sensor 45, and thecenter of the slit 480 and the width center of the light-receivingportion of the image sensor 45 are allowed to be coincident with eachother. By performing the image sensor alignment operation described withreference to FIG. 5 in the first embodiment, as illustrated in FIG.10(c), the amount of change of the brightness with respect to themovement in the X direction of the sensor can be increased.

According to the embodiment, the position information of the detecteddefect can be extracted at a higher accuracy.

Fourth Embodiment

A configuration of a defect inspection device 1100 according to a fourthembodiment is illustrated in FIG. 11. The configuration of the defectinspection device 1100 according to the embodiment is basically the sameas the configuration according to the first embodiment described withreference to FIG. 1. The configuration is different from that of thefirst embodiment in that the plane mirror 24 in the first embodimentwhich is arranged to be taken in/out between the ¼-wavelength plate 20and the plane mirror 25 to change the optical path in the verticalillumination system 203 is replaced with a half mirror 24′ in theembodiment, and the half mirror 24′ is fixedly installed between the¼-wavelength plate 20 and the plane mirror 25.

According to such a configuration, in the embodiment, the obliqueillumination system 201 and the vertical illumination system 203 aresimultaneously operated to illuminate the wafer 1. In the embodiment, inthe configuration illustrated in FIG. 11, the illumination area of thethin-line illumination light 35 by the oblique illumination system 201on the wafer 1 and the illumination area of the thin-line illuminationlight 36 by the vertical illumination system 203 are spatially separatedwithin the field of view of the objective lens 40 and simultaneouslyilluminated. The scattered light generated from the illumination area ofthe thin-line illumination light 35 by the oblique illumination system201 is collected by the objective lens 40 and detected by the imagesensor 45.

The scattered light generated from the illumination area of thethin-line illumination light 36 by the vertical illumination system 203performing the vertical illumination through the objective lens 40 isdetected through the objective lenses 50 and 60 by the image sensor 55and 65. By doing so, a type of defects generating strong scattered lightby the oblique illumination and a type of defects generating strongscattered light by the vertical illumination can be simultaneouslydetected. As a result, the two times of inspection of the related artwhich are divided with different illumination conditions can besimultaneously performed in one time of inspection, so that a time ofinspection can be reduced.

In this case, the method of position alignment of the image sensor 45with the irradiation position of the oblique illumination light 35 onthe pattern chip 150 and the method of position alignment of the imagesensors 55 and 65 with the irradiation position of the verticalillumination light 36 on the pattern chip 150 are the same as those ofthe first embodiment. In addition, in the image sensors 45, 55, and 65,the scattered light of any one of the oblique illumination and thevertical illumination can be detected by any combination of the imagesensors.

According to the embodiment, since the defect detection by the obliqueillumination and the defect detection by the vertical illumination canbe simultaneously performed, the throughput of detection can be improvedin comparison with the method of switching the direction of illuminationto sequentially perform the defect detection by the oblique illuminationand the defect detection by the vertical illumination.

Various combinations of the configurations and functions of theembodiment described above can be considered. It should be noted thatthese combinations are also included with the scope of the invention.

EXPLANATIONS OF LETTERS OR NUMERALS

-   -   1: wafer    -   5: laser    -   7: shutter    -   9: beam expander    -   10: plane mirror    -   16: ½-wavelength plate    -   20: ¼-wavelength plate    -   25: plane mirror    -   30: cylindrical condenser lens    -   40, 50, and 60: objective lens    -   41, 51, and 61: imaging optical system    -   45, 55, and 65: image sensor    -   47, 57, and 67: optical-axis-direction driving mechanism for        image sensor    -   49, 59, and 69: vertical-to-optical-axis direction driving        mechanism for image sensor    -   75: image processing unit    -   80: operation system    -   85: mechanical system control unit    -   100: stage unit    -   130: height detection unit for autofocusing    -   150: pattern chip    -   171: image plane observation camera    -   200: illumination optical system section    -   201: oblique illumination system    -   202, 203: vertical illumination system    -   300: detection optical system section    -   400: AF detection system    -   1000, 1100: defect inspection device

1. A defect inspection device for inspecting a sample, comprising: amovable table on which the sample as an inspection object and a patternchip with periodic patterns are mounted; an illumination lightirradiation unit which irradiates a surface of the sample or a surfaceof the pattern chip mounted on the table with linearly-formedillumination light; a detection optical system section provided with aplurality of detection optical systems which respectively focus or thepattern chip on an image sensor and detect an image of the scatteredlight; and an image plane observation camera provided on at least one ofthe detection optical systems which are disposed on the detectionoptical system section, wherein said detection optical system section isconfigured to inspect the sample by performing an image-focusingcorrelation among the pattern chip surface, a focus of the illuminationlight, and respective image sensors of the plurality of detectionoptical systems disposed on the detection optical system section isestablished by positioning the pattern chip with a height where a heightof a focal plane of an objective lens of the respective detectionoptical systems is coincident with a surface height of the pattern chipcalculated by means of the image plane observation camera;focus-adjusting the illumination light irradiation unit andposition-aligning a short axial direction of the linearly-formedillumination light using the image plane observation camera; andposition-aligning the respective image sensors of the plurality ofdetection optical system section to an optical axis direction and to theshort axial direction of the linearly-formed illumination light. 2-12.(canceled)
 13. The defect inspection device according to claim 1,wherein the image plane observation camera is a two-dimensional camera.14. The defect inspection device according to claim 1, wherein at thestep of position-aligning the respective image sensors of the pluralityof detection optical systems disposed on the detection optical systemsection to the short axial direction of the linearly-formed illuminationlight, a slit thinner in width than a short axis of the image of thescattered light generated from the sample or the pattern chip which isirradiated with the linearly-formed illumination light and detected bythe image sensor is arranged in front of the image sensor.
 15. Thedefect inspection device according to claim 1, wherein plural kinds ofpatterns are formed on the pattern chip.
 16. A defect inspection methodfor inspecting a sample, comprising: irradiating, using an illuminationlight irradiation unit, a surface of the sample or a surface of thepattern chip mounted on a movable table with linearly-formedillumination light; focusing scattered light generated from the sampleor the pattern chip using a detection optical system section providedwith a plurality of detection optical systems each of which respectivelyfocus said scattered light generated from the sample or the pattern chipon an image sensor; detecting an image of the scattered light; andinspecting the sample using an image plane observation camera providedon at least one of the detection optical systems which are disposed onthe detection optical system section, wherein said inspecting furthercomprises performing an image-focusing correlation among the patternchip surface, a focus of the illumination light, and respective imagesensors of the plurality of detection optical systems disposed on thedetection optical system section is by performing a step of positioningthe pattern chip with a height where a height of a focal plane of anobjective lens of the respective detection optical systems is coincidentwith a surface height of the pattern chip calculated by means of theimage plane observation camera; a step of focus-adjusting theillumination light irradiation unit and position-aligning a short axialdirection of the linearly-formed illumination light by means of theimage plane observation camera; and a step of position-aligning therespective image sensors of the plurality of detection optical systemsection to an optical axis direction and to the short axial direction ofthe linearly-formed illumination light.
 17. The defect inspection methodaccording to claim 16, wherein the image plane observation camera is atwo-dimensional camera.
 18. The defect inspection method according toclaim 17, wherein the step of position-aligning the respective imagesensors of the plurality of detection optical systems disposed on thedetection optical system section to the short axial direction of thelinearly-formed illumination light, further comprises forming a slitthinner in width than a short axis of the image of the scattered lightgenerated from the sample or the pattern chip which is irradiated withthe linearly-formed illumination light and detected by the image sensor,and wherein the slit is arranged in front of the image sensor.
 19. Thedefect inspection method according to claim 18, further comprisingforming plural kinds of patterns on the pattern chip.